188 THE SUN — ITS CHEMICAL ANALYSIS. 



it could not long remain so bright as it appears to us and as it ap- 

 peared to our most remote ancestors. The heat which it loses by 

 radiation is truly enormous. M. Pouillet has calculated that during 

 each second it gives out 13,300 calories, that is to say, 13,300 times 

 the quantity of heat necessary to raise one gram of water from zero 

 to 75 degrees C. Would we have an idea more easily appreciable of 

 that quantity of heat? Employed to exert a mechanical effect, it 

 would be sufficient to raise a weight of 5,600,000 kilograms to an 

 altitude of one metre. 



This expenditure of heat is so enormous that the surface of the 

 sun would, witliout doubt, soon become obscure if the process went 

 on without variation, and nothing returned to the sun the heat which 

 it is constantly losing. Now, whence is derived this heat thus con- 

 tinually renewed ? Can we imagine that it results from a chemical 

 combination, from the combustion of different substances ? If the sun 

 were a mass of incandescent charcoal, it has been computed that 

 1,200 kilograms of that body would be consumed every hour for each 

 square metre. If the central orb was of the same composition as our 

 gunpowder, during each minute a layer of powder one metre in thick- 

 ness would be burnt, and our present sun would disappear in nine 

 thousand years. On the same hypothesis the solar diameter would 

 eight thousand years ago have been double what it is to-day. I pre- 

 sent these singular suppositions only to make it apparent that the 

 phenomenon of the solar heat perpetually maintained cannot be com- 

 pared with the phenomena of combustion, with which our experience 

 is most familiar. We must prepare our minds for something extra- 

 ordinary when the question relates to that immense focus whose 

 activity seems never to slacken. Everything leads us to believe that 

 the sun does not consume itself alone, but that it receives incessantly 

 from without, new materials, which are precipitated into its orbit and 

 there become incandescent. Let us suppose that the sun is encom- 

 passed by an immense cosmic ring formed of a multitude of meteorites. 

 Attracted by the powerful mass of the sun, these meteors will describe 

 spirals more and more closely approaching the centre with a velocity 

 always increasing. Arrived in the solar atmosphere, they will fall 

 upon the sun Avith the prodigious velocity which gravitation will com- 

 municate to them, a gravitation which at the surface of the sun is 

 twenty-eight times greater than at the surface of the earth. The 

 swiftness of a meteor arriving at the sun exceeds 600 kilometres a 

 second; supposing that it has entered the solar atmosphere with the 

 frozen temperature of the interplanetary spaces, we see that it must 

 there promptly be raised to temperatures higher than we can imagine. 

 M. Thomson, a learned Englishman, at once a mathematician and phys- 

 icist, has calculated that to maintain the actual solar heat it would 

 suffice that there should fall every year into the solar focus a quantity 

 of meteoric matter which would cover the surface of the sun to the 

 thickness of nine metres. Suppose, if you will, that twice as much is 

 necessary, that every year the level of the solar seas is raised eighteen 

 metres by virtue of this continual rain of incandescent meteors, it 

 would require four thousand years in order that the apparent, diameter 



